The present invention relates generally to control valves for fluid systems. More particularly, the invention relates to an electrically actuable dual diaphragm valve which assures the valve seat is closed by using the force developed by pressure from a first reservoir acting on a first diaphragm to offset the force developed by pressure from a second reservoir acting on a second diaphragm. The mechanical advantage of the first diaphragm over the second diaphragm is such that the desired valve seating is insured.
There are flow control valve applications which require a low differential pressure across the valve orifice and that can dictate that the valve orifice must be large. A large valve orifice can, in turn, dictate a large solenoid force acting against a large valve spring, in order to move the comparatively large valve body to the seated or unseated position. In many applications, the large solenoid needed for this purpose is prohibitive from a size, cost and electrical current requirement standpoint. Moreover, the large valve body of conventional design tends to be massive and comparatively sluggish and thus unsuited to fast response applications. Thus, it has heretofore been difficult and expensive to provide a fast response control valve which is capable of operating at high pressures and at high flow rates and which maintains a low differential pressure across the valve orifice.
One application which would benefit from a fast response control valve capable of handling high pressures and high flow rates is in the control of vehicular suspension systems by active electronic means. In these so-called active air suspension systems, electronic circuits can be devised to sense and respond to a road condition input (such as a road bump). If a suitably fast control valve were available, this electronically sensed road condition input could be used to control the suspension system to compensate for and minimize the impact felt by the vehicle occupants. Such a suitably fast control valve has heretofore been impractical, due in part to the need for a large solenoid and massive valve body to handle the required high pressures and high flow rates.
The present invention provides a control valve system which is well suited to the active air suspension system for vehicles and for other applications where high pressures and high flow rates are involved and where a fast response is desired. The control valve system is thus adapted for connection between a first reservoir (such as the air suspension system tank) and a second reservoir (such as the air suspension system reservoir).
The valve system employs a valve housing having a first conduit in communication with the first reservoir and a second conduit in communication with the second reservoir. A cavity is disposed in the valve housing in communication with the first and second conduits. Within the cavity is a diaphragm/valve body system comprising a first diaphragm and a second diaphragm, each preferably being mechanically coupled or integrally formed with a valve body member. The valve system includes a valve orifice within the housing which communicates with the first conduit. The valve body is disposed within the cavity and positioned where it can movably seat and unseat on the valve seat defined by the valve orifice.
The first diaphragm is connected to the sidewalls of the valve housing and defines a first chamber, the first chamber preferably being a portion of the cavity within the housing. The second diaphragm is also preferably connected to the sidewalls of the valve housing. The second diaphragm is arranged generally parallel to and spaced apart from the first diaphragm. The first and second diaphragms define between them a second chamber which is vented, preferably to atmosphere, by a venting means in the housing. The venting means may be in the form of an aperture through the sidewall of the housing which communicates with the second chamber.
The control valve system further comprises an electrically actuable means coupled to the first chamber and to the first conduit means for selectively assuming at least two states. The electrically actuable means assumes a first state in which the first chamber is coupled to the first conduit means and a second state in which the first chamber is vented. Preferably in the second state the first chamber is vented to atmosphere or to the same pressure condition as the second chamber is vented. The valve body associated with the first and second diaphragms is responsive to the first and second states of the electrically actuable means. When the electrically actuable means is in its first state, the valve body is seated on the valve seat, preventing flow between the first and second reservoirs. When the electrically actuable means is in the second state, the valve body is unseated from the valve seat, permitting flow between the first and second reservoirs.
The electrically actuable means is preferably a two-state solenoid valve which can be designed to toggle between states at high speeds. The preferred solenoid valve is also suitable for receiving pulse width modulated activation signals as will be explained more fully below.
The average surface area of the first diaphragm is greater than that of the second diaphragm. When the electrically actuable means is in the first state, fluid pressure is delivered to the first chamber where it acts on the first diaphragm, forcing the first diaphragm and valve body into the seated position. The relatively large surface area of the first diaphragm establishes a mechanical advantage such that the forces acting to seat the valve body are greater than the forces acting to unseat the valve body caused by pressure on the second diaphragm. Preferably the first chamber is fashioned to contain a minimal volume, sufficient to permit movement of the valve body to the unseated position. The minimal volume allows the first diaphragm to respond to comparatively small pressure changes at relatively fast response times. In effect, the second diaphragm isolates the first diaphragm from the pressures within the second reservoir. This allows the first diaphragm to operate at high speeds and still produce sufficient force to seat the valve body on a large valve orifice.
For a more complete understanding of the invention, its objects and advantages, reference may be had to the following specification and to the accompanying drawings.